Rate transmittal method for beamrider missile guidance

ABSTRACT

In beamrider guidance of a missile toward a target, tracking or error determination is accomplished on board the missile. Rate information obtained at the launch site must be transmitted to the missile if it is to be used in the guidance thereof. Rate information allows correction of the inherent lag of a missile behind the target line-of-sight. A method of electronically accomplishing the equivalent of an optical boresight shift allows the missile direction to be adjusted to compensate for the inherent lag of the missile as it moves toward the target.

United States Patent Miller, Jr. et al.

[451 Apr. 30, 1974 RATE TRANSMITTAL METHOD FOR BEAMRIDER MISSILEGUIDANCE Inventors: Walter E. Miller, Jr.; Jimmy R.

Duke; Robert L. Sitton, all of Huntsville, Ala.

The United States of America as represented by the Secretary of theArmy, Washington, DC.

Filed: Oct. 20, 1972 Appl. No: 300,558

Assignee:

U.S. Cl. 244/113 Int. Cl F41g 7/14, F42b 15/02, F42b 15/10 Field ofSearch 244/3. 1 3

References Cited UNlTED STATES PATENTS 6/1966 Hawes 244/3.l3

3,028,807 4/1962 Burton et al 244/113 Primary ExaminerBenjamin A.Borchelt Assistant Examiner-Thomas H. Webb Attorney, Agent, orFirm-Edward J. Kelly; Herbert Berl; Jack W. Voight [57] ABSTRACT Inbeamrider guidance of a missile toward a target, tracking or errordetermination is accomplished on board the missile. Rate informationobtained at the launch site must be transmitted to the missile if it isto be used in the guidance thereof. Rate information allows correctionof the inherent lag of a missile behind the target line-of-sight. Amethod of electronically accomplishing the equivalent of an opticalboresight shift allows the missile direction to be adjusted tocompensate for the inherent lag of the missile as it moves toward thetarget.

3 Claims, 4 Drawing Figures PATENIEBAPR so 1924 SHEEIIBFZ ON AXISMISSILE DISPLACED MISSILE PATENIEDnrnso m4 3Q807L658 sum 2 or 2 l I c005I i I 1 CODE 11 CODE m I f cooem 1 f l I RIGHT ERROR YAW SIGNAL E T IRJI 1 LEFT ERRoR I+nz-(n+mn ONE NUTATION CYCLE A FIG. 3

T|ME-- CODE I com: I f

CODEIIE T! CODE 11 I f f f f RIGHT ERROR 4 f YAW SIGNAL n oI+DZ-(1I+II1Z) U U 9 f f3 LEFT ERROR RATE TRANSMITTAL METHOD FORBEAMRIDER MISSILE GUIDANCE BACKGROUND OF THE INVENTION Beamriderguidance is a method of guidance whereby a missile is enabled todetermine its own relative position in a transmitted beam, due tospatial encoding of that beam. The missile generates guidance commandsto correct missile flight path toward the center of the transmittedbeam. A gunner then points the beam at a target, and the missile followsthe beam to target impact. Since the missile generates its correctionalcommands internally there is no requirement for correctional or trackingguidance from an external source.

However, the line-of-sight rate resulting from a moving target or amoving transmitter causes a missile guidance error. This guidance erroris defined as lag of the missile behind the changing line-of-sight ofthe transmitted beam. Since this changing line-of-sight may be measuredat the transmitter as an angular rate, it can be used to reduce themissile guidance error caused by line-of-sight rate. Since guidancecommands are generated on board the missile, any rate information musteither be transmitted directly to the missile, or be used to alter theboresight of the transmitter to compensate for predicted missile lag.Rate transmission requires either a separate transmission link or amultiplexing method. Mechanical or optical boresight shift mechanismsare not capable of providing the $0.1 milliradian accuracy required.

A beamrider missile guidance method and apparatus are disclosed inpatent application Ser. No. 275,014, filed July 25, 1972 by Miller etal. Miller et al. disclose an improved beamrider missile guidance systemwherein an observer at a launch site visually locates a target. AIine-of-sight to the target is established through a telescopic sight.An optical transmitter, boresighted to the telescope, directs opticalenergy toward the target. Transmitted optical energy is spatiallyencoded to allow on board missile sensors to respond to missiledeviation from the observers line-of-sight to the target. Errorinformation generated in the missile allows automatic missilecorrectional commands for returning the missile to the line-of-sight.

SUMMARY OF THE INVENTION In a beamrider missile guidance system a movingtarget is tracked by visual line-of-sight from the target trackingstation or launch site. The missile is launched substantially along theline-of-sight axis to the target. Rate transmission for beamriderguidance is encoded into the existing guidance information with the samecode or frequencies already present in the beam. The transmitted beam,formed of individually modulated beam segments, has one or more segmentsmodified by alternately modulating the segment with the modulation rateof an adjoining segment. This alternate modulation of adjoining segmentsprovides electronic adjustment of the optical boresight so that the beamnull is leading the target by an amount equivalent to the inherentmissile lag, the missile trajectory is effectively corrected to placethe missile directly on target. Thus, missile trajectory is corrected atthe tracking station without transmitting any additional signals in thebeam.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an embodiment of thebeamrider guidance system.

FIG. 2 is a static cross-section of a four-quadrant beam having fourcodes or frequencies for respective quadrants.

FIG. 3 is a diagram of the signal resulting on the missile for on-axisconditions without rate encoding.

FIG. 4 is a signal diagram resulting on the missile for on-axisconditions with rate encoding included.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,FIG. 1 discloses an optical beamrider system. A target tracking station10 directs an optical beam from a source 12 toward a target 14. Source12 is boresighted to follow telescopic tracking of the target by anobserver or gunner at the tracking station. A missile 16 is launchedinto the path of beam 18 toward the target. An optical receiver 19 onthe missiles aft end responds to the spatially encoded light beam 18 fordirecting the missile toward the center of the beam. The beam center isthe line-ofsight axis 20 between target tracking station 10 and target14.

FIG. 2 discloses the cross-sectional beam pattern of a static beam.Separate beams I, II, III and IV are brought together in quadrants toform the single beam 18. These beam segments are coded to distinguishrespective quadrants. The four-quadrant beam is nutated in space with anutation radius equal to approximately one-half the beam radius. Themissile detector 19 then sees, sequentially, the four codes(frequencies) of the four quadrants, with a duty factor that isdependent on missile location within the beam. This duty factor providesmeasurement of missile position error in the beam.

Typical of ideal conditions a missile is shown in dotted lines centeredon axis for the four-quadrant beam of FIG. 2. As the beam is nutated,the missile will sequentially receive the codes of quadrant I, II, IIIand IV with equal duration of each quadrant (as also shown in FIG. 3).If, however, the missile is displaced to the right of the center therelative duration of codes I and IV will be increased and the durationsof codes II and III 'will be decreased. The missile error signal isdetermined from these relative durations. However crossing motion by thetarget or tracker results in a consistently displaced missile which iscontinuously seeking alignment. Missile displacement to the right asshown in FIG. 2 is caused by a right to left crossing target and theresulting line-of-sight rate. Correction of this lag with leadadjustment is accomplished by a shift of the boresight to the left. Theboresight shift is equal to the expected missile lag as determined bythe angular line-of-sight rate measured at the beam transmitter.

FIG. 3 shows the signal resulting on the missile for the on-axiscondition. Left to right missile position in the beam is given by therelative duration of the quadrants on the missile sensor 19. Thus, (Iand IV) (II III) provides the yaw signal where positive is right errorand negative is left error in the figure. If these durations are equal,the average yaw error is zero. Referring now to FIG. 4, the signal inquadrant II is modified to be an alternating code frequency f (code I)for a short time, and code II or frequency f for a short time. This prolll duces, for an on-axis missile, the yaw signal of FIG. 4. A positiveor right error has been indicated, since the average yaw signal ispositive. Thus, the boresight axis has shifted. By making the boresightaxis shift approximately equal to the error caused by the line-of-sightrate, correction for this error is accomplished. Missile electronicsrespond to the signals received by detector 19, sensing the relativetime duration of respective pulses and combining these signals toactivate correctional guidance. Thus the missile is directed to lead atarget by the equivalent amount of lag caused by the lineof-sight rate,thereby placing the missile directly on axis with the actual target.Reversal of the inter-modulation, f into quadrant I, would be used forlead in the opposite direction.

Quadrants III and IV can also be used for boresight shifting, in orderto make the shift in yaw independent of missile pitch errors. Codes 1,II, III and IV may easily comprise separate frequencies f f f and fallowing simplified detection of time duration signals.

Although a particular embodiment and form of this invention has beenillustrated, it is readily apparent that various modifications andembodiments of the invention may be made by those skilled in the artwithout departing from the scope and spirit of the foregoing disclosure.For example, since all four quadrants can be intermodulated, otherbiases can be corrected for. Thus, a gravity bias can be programmed toprovide missile lift as a function of expected missile velocity (time),and wind velocity can be measured and corrected for if desired.Accordingly, the scope of the invention should be limited only by theclaims appended hereto.

We claim:

1. In a beamrider missile guidance system wherein a target is tracked byvisual line-of-sight from a tracking station and the missile is directedtoward said target substantially along the line-of-sight axis, a methodof transmitting rate information within the beam path and comprising thesteps of:

directing optical energy from said target tracking station along theline-of-sight to the target,

spatially encoding said optical energy for providing a plurality ofindividually modulated optical frequency beams,

forming said individually modulated beams into a single beam ofadjoining segments, and

modifying at least one of said beam segments by alternately modulatingthe beam segment with the modulation rate of an adjoining segment. 2. Ina beamrider missile guidance system a method of transmitting rateinformation within the beam path as set forth in claim 1 and furthercomprising the steps of:

forming said beam segments into a quadrant, nutating said beam forsequentially sweeping a portion of respective quadrants across themissile directed toward said target, and

alternately modulating said modified beam segment with a portion of saidadjoining segment signal modulation which portion is equal in magnitudeto missile lag.

3. In a beamrider missile guidance system a method of transmitting rateinformation within the beam path as set forth in claim 2 and furthercomprising the step of: detecting by said missile the duration ofrespective quadrant modulation rates during nutation for the furtherstep of controlling the error correction of the missile trajectorytoward said target.

1. In a beamrider missile guidance system wherein a target is tracked byvisual line-of-sight from a tracking station and the missile is directedtoward said target substantially along the line-of-sight axis, a methodof transmitting rate information within the beam path and comprising thesteps of: directing optical energy from said target tracking stationalong the line-of-sight to the target, spatially encoding said opticalenergy for providing a plurality of individually modulated opticalfrequency beams, forming said individually modulated beams into a singlebeam of adjoining segments, and modifying at least one of said beamsegments by alternately modulating the beam segment with the modulationrate of an adjoining segment.
 2. In a beamrider missile guidance systema method of transmitting rate information within the beam path as setforth in claim 1 and further comprising the steps of: forming said beamsegments into a quadrant, nutating said beam for sequentially sweeping aportion of respective quadrants across the missile directed toward saidtarget, and alternately modulating said modified beam segment with aportion of said adjoining segment signal modulation which portion isequal in magnitude to missile lag.
 3. In a beamrider missile guidancesystem a method of transmitting rate information within the beam path asset forth in claim 2 and further comprising the step of: detecting bysaid missile the duration of respective quadrant modulation rates duringnutation for the further step of controlling the error correction of themissile trajectory toward said target.